Modulating system



May 4, 1937.

FIG.

R. R. RlESZ MODULATING SYSTEM Filed July 7, 1956 BPF. gm

BPF

UM/$44 M TTORNEV ing a Wheatstone-bridge network lll which is PatentedMay 4, 1937 Q umrlzn anew 2,078,974 MODULATING SYSTEM Robert RaRiesz,Mount Vernon, N. Y., assignor to BellTelephoneLaboratorics,Incorporated, New

York, N. Y., acorporation of New York ApplicationJulyfl; 1936, SerialNo. 89,363

This invention relates to modulating systems, and moreparticularl-ytomodulating systems employing physically inert non-linear; resistanceapplying a signaling voltage across the points 2| elementsas-modulatingapparatus;

an; object of the inventionls to; obtain incircuitlof amodulatingsystem;'

creased suppression of the an'ier in the output Inapreferred-embodiment;theinvention coma prises plurality "of physicallyinert'-'non-'linear.'

resistance elements arrangediin the form of a Wheatstone bridge in l la" modulating, system to effect: signal 'modulation of carrier waves.relatively small"resistance connected in series in one carrierconductive arm and arelatively large in the output circuit.

Theinvention'will'be more fully comprehended from the. followingdescription taken together with the accompanying drawing in "which:

Fig; 1 illustrates a preferred embodiment of the invention; and

Fig. 1A shows one'modification' of-the invention;

Figs. 13, 1C and 1D illustrate-other modifications of the invention.

Fig. 1 illustrates a modulatingsystem-embody connectedin shunt withfilters ll 'and l2f The filter I l adapted to pass a band of modulatingfrequencies produced-at'a signaling source I3 is directly connected tothe output filter l2. A load M is connected across the output filter 12which is adapted to pass side-band frequencies lying adjacent to thecarrier vfrequency produced by a generator l5. Leads l9 and 20connecting filters l l and 12 are also joined to points 2i and 22 of thebridge network l0 whose points 24 and 25 are connected to filter 23associated with the carrier generator l5.

The Wheatstone bridge network It! comprises physically inert non-linearresistance elements 29, 30, 3| and 32. These may be of any suitablenon-linear type, such, for example, as copperoxide rectifiers or othernon-linear resistors of suitable type. The rectifiers are poled asindicated by the arrows in Fig. 1, such that nonlinear resistanceelements 29 and 30 are poled in a carrier non-conductive directiontoward common terminal 24 while non-linear resistance elements 3| and 32are poled in a carrier conductive direction away from common terminal25.

Theoperation of. the W'heatstone bridge in a modulating system iswell-known and consists in voltages together with the non-linearresistanceelements produce a modulation actionzwhereby thecarrier-;cur-rents and signaling currents are combined in the well-knownmanner to effect a signal modulation of thecarrier Wave of the carriersuppressed type. This is most efficiently accomplished, when thenon-linear resistance elements comprising the bridge network.-barebalanced to a high degree of precision in both the conductive andnon-conductive directions with respect to carrier.

In a preferred embodiment, the invention comprises a variable resistance33 connected in series with the non-linear resistance element 3| of'aconductive arm and a variable resistance 34 connected in shunt with thenon-linear resistance element 32 ofa non-conductive arm, the termsconductive and-non-conductive being used with reference toi the carrierwave.

By a use of= theseresistances an accurate balancemfthe bridge network.in in the conductive and non-conductive directions may be obtained J asfollows.-

ance 3|. is varied to producethe best. bridgebalance ,forthe conductivedirection, Also, with no signalcurrent but with the carrier currentflowing in the non-conductive direction, resistance 34 is varied toeffect the most accurate bridge balance for the non-conductivedirection. Accordingly, by alternate adjustments of the resistances 33and 34, the bridge network ll! may be eventually balanced to a highdegree of precision. Obviously, a precise balance is desirable so as toobtain maximum suppression of carrier waves in the output circuit.

It will be noted, however, that resistance 33 is effective in only onearm in the conductive direction and one arm in the non-conductivedirection, and further, that shunt resistance 34 is effective inconnection with but one arm of the non-conductive direction. Inasmuch asresistance 33 has a relatively low value of the order of 5 ohms, it willnot appreciably affect the balance in the non-conductive direction.Likewise, since resistance 34 has a relatively large value of the orderof 5500 ohms, it will not appreciably influence the balance in theconductive direction.

It will be understood that the same result is also attained when theresistance 33 is connected in series with either resistance element 3|or 32 and the resistance 34 in shunt with either the resistance element3| or 32. Bridge circuits embodying these modifications are shown inFigs. 13, 1C and 1D.

The connection of the series resistance 33 and shunt resistance 34 inthe above combinations depends on the conducting and non-conductingresistance values of the non-linear resistance elements. The respectiveresistance values may be indicated as follows: In balancing a Wheatstonebridge, it is essential that Then in the conducting direction,

- 322 If 30 3l resistance 33 is inserted in series with resistanceelement 3|; and 29 53 if ao 3i resistance 33 is placed in series withresistance element 32.

Similarly, in the non-conducting direction,

resistance 34 is connected in shunt with resistance element 32; and 522E If ao R31 resistance 34 is connected in shunt with resistance element3|.

Fig. 1A illustrates a modified Wheatstone bridge network 35 that may besubstituted for the bridge network ID of Fig. 1. In Fig. 1A, apotentiometer 36 is interposed between the non-linear resistanceelements 3| and 32 poled in the conductive direction away from contactpoint 25. By this arrangement, the conductive arms containingresistances 3| and 32 may be varied simultaneously. Further, it is seenthat the potentiometer 36 is effective in both non-conductive arms aswell as both conductive arms. The potentiometer 36 has a relativelysmall resistance; therefore it will not appreciably afiect the balancein the non-conductive direction. Likewise, the resistance 34 isrelatively large, hence it will not appreciably afiect the balance inthe conductive direction.

In Fig. 1A, the resistance 34 may be connected in shunt with eitherresistance element 3| or 32 depending on the non-conducting resistancevalues of the non-linear resistance elements as illustrated aboverelative to Fig. 1.

It will be understood, of course, that the bridge networks l0 and 35 maybe balanced to a high degree of accuracy in a minimum of time when thefour non-linear resistance elements are substantially identical.

What is claimed is:

1. A modulating system of the carrier suppressed type comprising asource of modulating Waves connected in an input circuit of the system,an output circuit, a balanced Wheatstone bridge comprising a physicallyinert non-linear resistance element in each of its arms, the Wheatstonebridge being interposed between the input and output circuits, a sourceof carrier Waves connected to the Wheatstone bridge for modulationtherein by said modulating waves, and means for increasing the degree ofsuppression of the unmodulated carrier component by providing a moreaccurate bridge balance than is afiorded by balancing saidnon-linearresistance elements against one another comprising aresistance connected in series with a non-linear element in one arm ofthe bridge and a resistance connected in shunt relation to thenon-linear element in a different arm of the bridge, said series andshunt resistances being proportioned to provide the required degree ofbalance.

2. A modulating system according to claim 1 in which the seriesresistance has such a value as will unappreciably affect the bridgebalance in the non-conductive direction while the shunt resistance has avalue that will unappreciably affect the bridge balance in thenon-conductive direction while the shunt resistance has a value thatwill unappreciably affect the bridge balance in the conductivedirection.

3. A modulating system according to claim 1 in which the resistanceconnected in series in an arm is in series with one of the non-linearresistance elements poled in a conductive direction away from a commonterminal.

4. A modulating system according to claim 1 in which the resistanceconnected in series is a potentiometer interposed between the twononlinear resistance elements poled in the conductive direction awayfrom a common terminal.

ROBERT R. RIESZ.

